1. Field of the Invention
The present invention relates to the photolithography process used to manufacture semiconductor devices, for example. More particularly, the present invention relates to a method of manufacturing a phase shift mask of a photolithographic exposure apparatus.
2. Description of the Related Art
A photolithography process for fabricating a micro circuit (pattern) on a wafer is a principal part of a semiconductor manufacturing process. In addition, the quality of the photolithography process is a major factor influencing the quality and yield of semiconductor chips.
The photolithography process employs a mask by which a micro pattern can be transferred to a wafer. In general, a chrome mask is used. The chrome mask comprises a chrome pattern formed on a quartz substrate. However, due to the way in which it diffracts light, a basic chrome mask cannot be used in providing the higher degree of resolution required to meet today's demand for highly integrated chips. The phase shift mask has been developed to overcome such limitations.
There are various kinds of phase shift masks. One type of phase shift mask is a chromeless phase shift mask, which uses only a phase shifter (a phase shift pattern) to transcribe a micro pattern on a wafer. The phase shifter of the chromeless phase shift mask is formed by etching a mask substrate to a predetermined depth. In other words, the phase shifter constituting a phase shift area of the chromeless phase shift mask comprises a trench formed by etching the mask substrate to a predetermined depth.
However, when a photoresist film pattern is formed on a wafer using an exposure apparatus that employs a chromeless phase shift mask to this end, there is a difference between the critical dimension or critical dimension uniformity of the photoresist pattern and that of the phase shifter of the chromeless phase shift mask. The extent of this difference depends on the exposure apparatus or exposure conditions.
Accordingly, the specifications of the mask, including the critical dimension or the critical dimension uniformity of the phase shifter, must be adjusted after the mask is manufactured to, in turn, ultimately provide a mask that will form a photoresist film pattern having the desired critical dimension or the critical dimension uniformity.